Smoke filter plug and process and cigarette made therefrom

ABSTRACT

A porous filter plug for a smoking article comprising a tow of longitudinally extending fibers enclosed within a plug wrap and having a cavity molded in the outer surface at one end. The plug is formed by molding a conventional tow of thermoplastic filamentary material. In use, a portion of the smoke passes from end to end through the plug and the remainder passes through the channel formed by the cavity and then axially through the plug wrap and the plug.

United States Patent Harllee et al.

SMOKE FILTER PLUG AND PROCESS AND CIGARETTE MADE THEREFROM Inventors:Gloria C. llarllee, 605 Muirs Chapel Rd., Greensboro, NC. 27410; John D.Woods, 3051 Magazine Dr., Winston-Salem, N.C. 27106 Filed: Dec. 20, 1971Appl. No.: 209,797

US. Cl. 13l/l0.5, 131/261 B Int. Cl. A24d 01/04, A241 07/04, A24f 13/06Field of Search l3l/10.5, 261 B, 131/10.7, 10 R References Cited UNITEDSTATES PATENTS 8/1972 Labbe 13l/l0.5 X 10/1970 Berger et al. 13l/l0.5 X3/1972 Berger et al. 131/10.5 X 3/1963 Cobb et a1. 131/268 X [451 Aug.14, 1973 3,093,142 6/1963 Swerdlofi' et a1 131/268 X 3,370,594 2/1968Haslam l3l/l0.5 X 3,062,219 11/1962 Miller 131/l0.5

FOREIGN PATENTS OR APPLICATIONS 1,118,860 3/1956 France l31/l0.5

Primary Examiner-Robert W. Michell Av a!!! Eureka-91 1 fi-r rAttorney-Albert H. Pendleton, Fred 1. Williams et al. I

[5 7] ABSTRACT 7 A porous filter plug for a smoking article comprising atow of longitudinally extending fibers enclosed within a plug wrap andhaving a cavity molded in the outer surface at one end. The plug isformed by molding a conventional tow of thermoplastic filamentarymaterial. In use, a portion of the smoke passes from end to end throughthe plug and the remainder passes through the channel formed by thecavity and then axially through the plug wrap and the plug.

14 Claims, 4 Drawing Figures SMOKE FILTER PLUG AND PROCESS AND CIGARETTEMADE THEREFROM BACKGROUND OF THE INVENTION This invention relates to aporous filter plug for a smoking article, to a process of making theplug, and to a cigarette which incorporates the plug as an essentialelement.

Most commercially available cigarette filters are limited in theirperformance characteristics. For example, conventional cellulose acetatefiber filters remove only 40 to 45 percent of the particulate materialin the smoke when the pressure drop across the filter is around 2.0 to2.5 inches of water. An increase in particulate material removalefficiency may be obtained by increasing the pressure drop across thefilter but a high pressure drop is objectionable and not acceptable tothe majority of smokers.

The filter described in U.S. Pat. No. 3,533,416 is in some respects anexception to the general rule concerning cellulose acetate fiber filterssince the performance of that filter is high at an acceptable pressuredrop and the smoke from the cigarette has a good taste. However, thefilter disclosed in that patent is difficult to produce and requires theuse of an excessive amount of filter material. As a result, it iscomparatively expensive to manufacture.

The prior art is replete with various proposed structures for filteringcigarette smoke under conditions which wil provide high efficiency at alow pressure drop. However, most all of these, and particularly thosewhich have been disclosed in the patent literature, have not beencommercially adopted because they are too expensive to produce and arenot adaptable for production on high speed cigarette-making machines.

Accordingly, an object of this invention is to provide a filter for asmoking article which has a high efficiency for the removal of tars fromcigarette smoke at an acceptable pressure drop.

A further object of this invention is the provision of a tobacco smokefilter which may be prepared from a lesser quantity of filteringmaterial than has heretofore been necessary for the manufacture of ahigh efficiency filter.

A still further object of this invention is the provision of a filterand a process for making it which is readily adaptable for manufactureby high speed cigarettemanufacturing machines.

A still further object of this invention is the provision of a highefficiency filter which may be prepared from materials that are alreadycommercially used for the purpose with a minimum modification ofexisting equipment.

A still further object of this invention is the provision of a processfor making a filter plug from a thennoplastic filamentary or fibrousmaterial which involves a simple molding step which may be rapidlycarried out without concomitantly heating the material to such a degreethat it sticks to the mold during the forming operation.

Further and additional objects will appear from the followingdescription, accompanying drawing and the appended claims.

GENERAL DESCRIPTION OF THE INVENTION In accordance with this invention,a fiber filter has been provided for attachment to the downstream end ofa smoking article such as a cigarette in which the smoke passes bothlongitudinally and axially through the filter. A portion of the smokepasses longitudinally through the filter in a conventional manner fromone end to the other and a second portion of the smoke is divertedthrough a channel formed by a cavity molded in one end of the filterplug. More specifically, a filter plug is provided which comprises a towof longitudinally extending fibers exposed at opposed ends for thepassage of smoke therethrough from end to end. The plug is provided witha porous overwrap closely embracing the side wall of the tow between theends and the plug has a cavity molded in the plug wrap and in the sidewall providing at least one smoke channel in the exterior side wall ofthe plug extending longitudinally from one of the end walls to alocation spaced from the other (i.e., short of) of the end walls.Preferably, there are a plurality of longitudinally extending cavitiesmolded into the end of the plug and they are arranged incircumferentially spaced, parallel relationship. The porous plug wrap isformed of a non-thermoplastic material such as paper having a porosityof less than about two seconds and preferably between 0.1 and twoseconds. This porosity may be the natural" porosity of the paper or itmay be an artificial porosity resulting from mechanically orelectrically providing small holes or perforations in a paper of lesserporosity in order to increase its porosity to the indicated level.

The filter plug of this invention is assembled onto a cigarette or othersmoking article in a manner analogous to that currently being usedcommerically for attaching fibrous filters to tobacco rods. Thisprocedure essentially involves the attachment of the filter plug to thetobacco rod by tipping paper which comprises an essentially smokeimpervious sleeve overlying portions of the plug and the tobacco rod forholding them in assembled relationship. In the structure of thisinvention, the tipping paper overlies the cavity or cavities in theexterior surface of the filter plug and provides the smoke channel orchannels which accommodate that portion of the smoke which is not drawnfrom end to end throughout the entire length of the tow of the filter.

The fibrous material that is employed for making the tow comprising themain body portion of the filter plug of this invention is celluloseacetate or any other thermoplastic material that is known to be suitablefor making fibrous filters. In commercial operation, the denier of theindividual filaments is preferably between about 1.3 and I6 while thetotal denier of the tow is preferably between about 38,000 and 100,000.

As previously indicated, the plug wrap is preferably formed of anon-thermoplastic material such as paper, and in order to obtain acigarette having a tar removal efficiency of greater than 50 percent ata pressure drop of between 2 and 2.5 inches of water, the porosity ofthe paper is preferably less than about 2 seconds, most preferablybetween 0.1 and Zseconds. As suggested above, this porosity may be thenatural" porosity of the paper or an artificial porosity achieved bymechani cally or spark perforating a paper which is more impermeablethan that above specified. As is well known, the porosity of papers ofthis type is measured in terms of seconds, and as used herein, the termmeans the average number of seconds required for the displacement ofcubic centimeters of air through the dry paper in an area of 1.0 squareinch obtained by testing five specimens with the felt" side up and fiveadditional specimens with the wire side up.'The method employed for thispurpose has been standardized by the American Society for TestingMaterials and has received the ASTM designation D726-55T which is arevision of ASTM designation D726-48. This standard method has also beenrecognized by the Technical Association of Pulp and Paper Industry underTAPPI Tentative Standard T460m-49. Inasmuch as the porosity is ameasurement of the rate of flow of air in seconds through a sample ofdry paper, it will be apparent that papers having the greater porosityare valued in the lower number of seconds and the higher number ofseconds reflect the more impervious papers.

It will be appreciated that the performance characteristics of thefilter of this invention will be dependent in part not only upon thetype and the denier of the filamentary material and the tow but alsoupon the porosity of the plug wrap through which a portion of the smokeflows during smoking. In this connection, most flexibility is achievedif the total exposed area of the cavity or cavities through which aportion of the smoke passes is such that it is between about 1 and 15times (preferably between about 5 and times) the area presented by thefilter plug at the exposed end surface from which the cavities extend.In other words, it is preferred that the ratio of the total exposedsurface of the cavity or cavities to the exposed area of the end of thetow adjacent the cavities be between about I to l and to l, mostpreferably between about 5 to l and 10 to l. Also, it is preferred thatthe percentage of the total.surface area presented by the cavity orcavities with respect to the total side wall surface area of the filterplug'be within the range of from to 90 percent, and preferably in therange from 70 to 85 percent.

The filter plug of this invention is readily prepared by providing a towof filamentary or fibrous thermoplastic material having the appropriatedenier and overwrapped with the plug paper having the indicatedporosity. .The ends of the fibers or filaments are exposed at theopposite ends of the tow. The resulting assembly is subjected to a hotmolding operation to impress the cavity or cavities so that one end ofthe plug will have the desired cavity configuration molded into theoverwrap and the tow. This may be effected by plunging one end of theplug into a hot ring mold having a sealloped interior configuration buthaving a cross-section somewhat less than the overwrapped tow. A machinethat may be adaptedfor such a plunging operation is described in thecopending application of Beard et al. Ser. No. 171,448, filed Aug. 13,197i, and assigned to the same assignee as this application.Alternatively, the molding may be effected by clamping theoverwrappedtow between hot mold plates having the desired configuration.

DESCRIPTION OF THE DRAWING For a more complete understanding ofthisinvention, reference will now be made to the accompanying drawing inwhich:

FIG. 1 is a perspective view of a filter plug constructed in accordancewith one embodiment of this invention;

FIG. 2 is an end elevational view of the plug shown in FIG. 1;

FIG. 3 is a sectional view of one end of a cigarette constructed inaccordance with one embodiment of this invention using the plug shown inFIGS. 1 and 2 with the cavity end of the plug in an upstreamorientation; and

FIG. 4 is the same as FIG. 3 except that the plug is arranged with thecavity end in a downstream orientation.

With moreparticular reference to the drawings, the filter plug l0consists essentially of a tow 12 of cellulose acetate filaments orfibers arranged in a longitudinal direction. The ends of the filamentsin the tow are exposed at the opposite ends of the plug so that as smokeis drawn through the device at least a portion of it will flow throughthe filter from end to end in the conventional manner. The filter plug10 is generally cylindrical in shape and has essentially the samediameter as the tobacco section or rod 14 including cigarette paper towhich it is attached. The side walls of the plug 10 between the oppositeends are closely embraced by a plug overwrap 16 which is formed fromthin porous paper, preferably having a porosity within the rangepreviously indicated. In the drawing the relative thickness of the plugwrap is magnified in the interest of clarity. A plurality of cavities 18are molded in the plug wrap and in the tow at one end of the filterplug. In the modification shown in the drawings, there are six of thesecavities, extending longitudinally in parallel, circumferentially spacedrelationship. The cavities extend from one end of the plug to a positionshort of the opposite end and when overwrapped with smoke impervioustipping paper 20, as shown in FIGS. 3 and 4, provide smoke channels forthe flow of that portion of the smoke which does not pass throughout theentire length of the filter plug. It will be noted that in the end ofthe plug opposite the end containing the cavities, a portion of theporous wrap 16 is in 360 angle contacting non-spaced relationship withthe tipping paper or sleeve 20.

As previously indicated, the total exposed surface area presented by thecavities is that of the bottom, side and end walls of each which providethe total surface through which the smoke passes to or from thechannels. This surface is preferably 1 to 15, most preferably 5 to 10,times the end wall surface of the plug adjacent the cavities (i.e., theend wall seen in FIG. 2). Also, this total exposed cavity surface ispreferably between about 20 to 90 percent, most preferably to percent,of the total side wall surface of the plug.

In the modification shown in FIG. 3, the open ends of the channels 18are located adjacent thetobacco rod 14 so that during draw a firstportion of the smoke enters the end of the plug and passes from end toend therethrough while a second portion of the smoke passes directlyfrom the tobacco rod into the channels formed by the cavities l8 andthen through the porous paper plug overwrap l6 and into the tow 12 fordischarge through the downstream end. In FIG. 4 the plug has beenreversed so that the smoke stream divides after it is within the mainbody of the tow, a portion continuing its progress out through thedownstream end and the other portion being diverted or escaping throughthe porous plug wrap 16 and then into the channels formed by thecavities 18. In order to permit the desired flow of smoke through thechannels to an effective degree, the depth of the cavity or cavities(i.e., the distance from the bottom of the cavity 18 to the innersurface of the tipping paper 20) should preferably be greater than about0.004 inch and suitably about 0.008 inch.

Thus, it will be apparent that a filter plug for a cigarette has beenprovided which presents a large surface area for the introduction orwithdrawal of the smoke from the filter. One portion of this areaconstitutes the end wall of the tow forming the plug and another portionof this area is made up of the side walls of the cavities formed in theplug. By this structure the efficiency and pressure drop characteristicsof the filter may be readily adjusted over a wide range to satisfy adesired requirement. As indicated, this may be done by modifying thefilament and tow denier, the porosity of the paper plug wrap and thedimension and size of the cavity or cavities in the plug.

METHOD OF MANUFACTURE An important feature of this invention resides inthe ease with which the filter plug may be manufactured at high speedswith a minimum modification of presently existing cigarettemanufacturing machinery. As indicated, the tow per se is formed offilamentary thermoplastic material such as cellulose acetate containinga suitable plasticizer and the plug overwrap is a conventional highporosity paper which is normally used in the manufacture of filter plugfor fiber type filters. It has been discovered that this conventionalfilter plug is readily adaptable for use in preparing the modified plugof this invention by a simple molding operation. The method involvesproviding the tow of fibrous material overwrapped with the porous paperand then subjecting the composite to hot molding to the desiredconfiguration at a temperature and for a time sufficient to deform andset the thermoplastic material and paper overwrap to the desiredcavity-containing configuration. The'plasticizer plays an important rolein the heat setting properties of the thermoplastic material. Aplasticizer such as triacetin is used in amounts ranging from 3 topercent by weight of tow and preferably from 8 to 12 percent. The porouspaper overwrap permits the use of a relatively high mold temperaturesince it is not melted by the heat and it prevents direct contact of themold with the thermoplastic fibrous material. Thus, the heat of the moldrapidly sets the fibrous material in the desired and predeterminedconfiguration without melting. By use of the high temperature, suitablybetween l75 and 300 C., the dwell time in the mold may be reduced toless than one second. As previously indicated, it will be appreciatedthat the molding operation may be effected by plunging one end of thefilter plug through a ring-shaped heated mold having a reduced diameterand adapted to produce the desired configuration of the cavities in theend of the filter plug. If desired, the mold may be one which closesaround one end of the plug, or it may close around a central portion ofa 2 up" plug assembly followed by cutting through a center line to formtwo plugs, as will be apparent to one skilled in the art.

SPECIFIC EXAMPLE A l.6/45,000 denier cellulose acetate filter plug 25millimeters long and 8 millimeters in diameter was wrapped with paperhaving a porosity of 0.34 second and subjected to a molding operation togive a plug having the general appearance shown in the drawings. Toeffect the molding a metal ring with a scalloped design inside the ringand sized so as to permit the 8- millimeter diameter filter plug to besnugly inserted therein served as the mold. The metal mold was heated toabout 275 C. and the 25-millimeter long filter plug was quickly pushedinto the mold and withdrawn, the total dwell time being about one-halfsecond. The shape of the plug was permanently altered by the action ofthe hot mold to give six equally spaced, longitudinal channels20'millimeters long on the surface of the plug. The modified filter plugwas attached to a tobacco rod of the same diameter by means of tippingpaper with the modified end of the plug abutting the tobacco rod. Thepressure drop (P) across the filter was determined to be 2.35 inches ofwater (measured at a flow rate of 14.5 cubic centimeters per second) andthe exposed surface area associated with the longitudinal channels wasapproximately 340 square millimeters (equivalent to a ratio of about 7to l for the exposed surface area on the side of the plug versus theend). Machinesmoking under standard conditions resulted in a totalparticulate removal (TPM) efficiency (E) of 66.3 percent or an El? ratioof 28.2 The El? ratio for a conventional l.6/45,000 denier celluloseacetate filter plug smoked in the same manner was found to be 17.6 (74percent efficiency and a 4.20-inch pressure drop).

While the drawings and the specific example show cavities having anessentially U-shaped cross-section, it will be apparent that othercross-sectional shapes are possible and the shapeof the mold may take ona number of shapes, e.g., hexagonal, square, etc. The cavity in suchinstances comprises a discontinuity in the otherwise cylindrical surfaceof the plug which, when enclosed by the sleeve of tipping paper, definesthe necessary longitudinal passageway for the smoke in accordance withthis invention.

While several specific embodiments have been indi cated in theforegoing, it will be apparent that many modifications may be madewithout departing from the spirit and scope of this invention as definedin the appended claims.

We claim:

I. A filter plug for a smoking article comprising a smoke impervioussleeve embracing a porous tow of longitudinally extending thermoplasticfibers exposed at opposite ends for the passage of smoke therethroughfrom end to end and a thin non-thermoplastic porous wrap for said tow,embracing in contacting non-spaced relationship the side wall of saidtow between said ends, said wrap being in 360 angle contactingnon-spaced relationship with said sleeve for a substantial first portionof its length, said tow having a cavity molded in the wrap and said sidewall and providing a smoke channel defined by the exterior surface ofsaid wrap and a substantial second portion of the length of said sleeve,said channel extending from one of said ends to a location spaced fromthe other of said ends.

2. The filter recited in claim 1 wherein the porosity index of saidporous wrap is less than about 2 seconds.

3. The filter recited in claim 1 in which there are a plurality of saidcavities providing a, plurality of said smoke channels. v

4. The filter recited in claim 3 in which said channels are arranged inspaced, parallel, longitudinally extending relationship.

5. The filter recited in claim 3 wherein ratio of the surface areadefined by said cavities "to the surface area of said one end is betweenabout 1 to l and 15 to l.

6. A filter plug for a smoking article being in the form of a cylinderof essentially uniform cross-section throughout its length andcomprising a smoke impervious sleeve embracing a porous tow oflongitudinally extending thermoplastic fibers exposed at opposite endsfor the passage of smoke therethrough from end to end and a porous paperwrap for said tow, closely embracing in contacting non-spacedrelationship the cylindrical side walls of said tow between said ends,said wrap being in 360 angle contacting non-spaced relationship withsaid sleeve for a substantial first portion of its length, said paperwrap having a porosity index less than about 2 seconds, said tow havinga plurality of longitudinal, parallel, spaced cavities, molded in thepaper wrap and the side wall of said tow, providing smoke channels inthe cylindrical side wall of said tow defined by the exterior surface ofsaid wrap and a substantial second portion of the length of said sleeve,said channels extending from one of said ends to a location spaced fromthe other of said ends, and the ratio of the exterior surface areaspresented by said cavities to the exterior surface area of said one endis between about 1 to l and to l.

7. The filter recited in claim 6 wherein the percentage of the exposedsurface areas within said cavities is between about and 90 percent ofthe total side wall surface area of said tow.

8. The filter recited in claim 6 wherein the fibers are celluloseacetate filaments, the denier of the filaments is between about 1.3 and16 and the total denier of the tow is between about 38,000 and 100,000.

9. A cigarette comprising a tobacco section overwrapped with cigarettepaper, a porous filter plug positioned at one end of said tobaccosection, and a smoke impervious sleeve overlying portions of said plugand said tobacco section for holding them in fixed relationship, saidplug comprising a tow of longitudinally extending thermoplastic fibersfor the passage of smoke therethrough from end to end and a thinnonthermoplastic porous plug wrap, embracing and in contactingnon-spaced relationship with the side wall of said tow between the endsthereof, said plug having a cavity, molded in the plug wrap and saidside wall, said wrap being in 360 angle contacting non-spacedrelationship with said sleeve for a substantial portion of its lengthproviding a smoke channel defined by the interior surface of said sleeveand the exterior surface of said wrap extending from one end of saidplug to a location spaced short of the opposite end thereof whereby aportion of the smoke from the tobacco section passes through said towfrom end to end of said plug and another portion of said smoke passesthrough said channel, said porous plug wrap and a portion of the two insaid plug.

10. The cigarette recited in claim 9 wherein said one end of said plugfaces upstream.

11. The cigarette recited in claim 9 wherein said one end of said plugfaces downstream.

12. A cigarette comprising a tobacco section overwrapped with cigarettepaper, a porous filter plug positioned at one end of said tobaccosection, and a smoke impervious sleeve overlying portions of said plugand said tobacco section for holding them in fixed relationship, saidplug having a uniform cross-section substantially the same as that ofthe tobacco section throughout its length and consisting essentially ofa tow of longitudinally extending thermoplastic fibers for passage ofsmoke therethrough from end to end and a porous paper plug wrap, closelyembracing and in non-spaced contacting relationship with the side wallsof said tow between the ends thereof, said plug having a plurality oflongitudinal, parallel, circumferentially spaced cavities, molded in thepaper plug wrap and the side wAll of said tow, said wrap being in 360angle contacting non-spaced relationship with said sleeve for asubstantial portion of its length provlding a plurality of smokechannels defined by the interior surface of said sleeve and the exteriorsurface of said wrap extending from one end of said plug to a locationshort of the opposite end thereof whereby a portion of the smoke fromthe tobacco section passes through said tow from end to end of said plugand another portion of said smoke passes through said channels, saidporous plug wrap and a portion of the tow in said plug.

13. The cigarette recited in claim 12 wherein the porosity index of saidpaper plug wrap is between about 0.1 and 2 seconds.

14. The cigarette recited in claim 13 wherein the ratio of the exteriorsurface areas presented by said cavities in the plug to the exteriorsurface area of said one end wall is between about 1 to l and 15 to l.

Patent No.

lnventofls) Gloria C, Harllee and John D. Woods It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

TITLE PAGE:

Insert Assignee: R. J; Reynolds Tobacco Company Winston- Salem, NorthCarolina 27102 "Attorney Fred L Williams" should be Attorney n Fred T,Williams Column 6, line 19, insert a period after '28.2".,

Column 8, line 5 "two" should be tow line 25, "wAll" should be wall line28, "providing" should be providing Signed and sealed this 12th day ofFebruary 1974.

(SEAL) Attest:

EDWARD M.FLETCHER,JR.

Attesting Officer MARSHALL NN Commissioner of Patents F ORM PO-1050(10-69) uscoMM-oc scan-ps9 UV! OVIINNINT PRINTING OFFICE: 19. D-lGl-II

1. A filter plug for a smoking article comprising a smoke impervioussleeve embracing a porous tow of longitudinally extending thermoplasticfibers exposed at opposite ends for the passage of smoke therethroughfrom end to end and a thin nonthermoplastic porous wrap for said tow,embracing in contacting non-spaced relationship the side wall of saidtow between said ends, said wrap being in 360* angle contactingnon-spaced relationship with said sleeve for a substantial first portionof its length, said tow having a cavity molded in the wrap and said sidewall and providing a smoke channel defined by the exterior surface ofsaid wrap and a substantial second portion of the length of said sleeve,said channel extending from one of said ends to a location spaced fromthe other of said ends.
 2. The filter recited in claim 1 wherein theporosity index of said porous wrap is less than about 2 seconds.
 3. Thefilter recited in claim 1 in which there are a plurality of saidcavities providing a plurality of said smoke channels.
 4. The filterrecited in claim 3 in which said channels are arranged in spaced,parallel, longitudinally extending relationship.
 5. The filter recitedin claim 3 wherein ratio of the surface area defined by said cavities tothe surface area of said one end is between about 1 to 1 and 15 to
 1. 6.A filter plug for a smoking article being in the form of a cylinder ofessentially uniform cross-section throughout its length and comprising asmoke impervious sleeve embracing a porous tow of longitudinallyextending thermoplastic fibers exposed at opposite ends for the passageof smoke therethrough from end to end and a porous paper wrap for saidtow, closely embracing in contacting non-spaced relationship thecylindrical side walls of said tow between said ends, said wrap being in360* angle contacting non-spaced relationship with said sleeve for asubstantial first portion of its length, said paper wrap having aporosity index less than about 2 seconds, said tow having a plurality oflongitudinal, parallel, spaced cavities, molded in the paper wrap andthe side wall of said tow, providing smoke channels in the cylindricalside wall of said tow defined by the exterior surface of said wrap and asubstantial second portion of the length of said sleeve, said channelsextending from one of said ends to a location spaced from the other ofsaid ends, and the ratio of the exterior surface areas presented by saidcavities to the exterior surface area of said one end is between about 1to 1 and 15 to
 1. 7. The filter recited in claim 6 wherein thepercentage of the exposed surface areas within said cavities is betweenabout 25 and 90 percent of the total side wall surface area of said tow.8. The filter recited in claim 6 wherein the fibers are celluloseacetate filaments, the denier of the filaments is between about 1.3 and16 and the total denier of the tow is between about 38,000 and 100,000.9. A cigarette comprising a tobacco section overwrapped with cigarettepaper, a porous filter plug positioned at one end of said tobaccosection, and a smoke impervious sleeve overlying portioNs of said plugand said tobacco section for holding them in fixed relationship, saidplug comprising a tow of longitudinally extending thermoplastic fibersfor the passage of smoke therethrough from end to end and a thinnon-thermoplastic porous plug wrap, embracing and in contactingnon-spaced relationship with the side wall of said tow between the endsthereof, said plug having a cavity, molded in the plug wrap and saidside wall, said wrap being in 360* angle contacting non-spacedrelationship with said sleeve for a substantial portion of its lengthproviding a smoke channel defined by the interior surface of said sleeveand the exterior surface of said wrap extending from one end of saidplug to a location spaced short of the opposite end thereof whereby aportion of the smoke from the tobacco section passes through said towfrom end to end of said plug and another portion of said smoke passesthrough said channel, said porous plug wrap and a portion of the two insaid plug.
 10. The cigarette recited in claim 9 wherein said one end ofsaid plug faces upstream.
 11. The cigarette recited in claim 9 whereinsaid one end of said plug faces downstream.
 12. A cigarette comprising atobacco section overwrapped with cigarette paper, a porous filter plugpositioned at one end of said tobacco section, and a smoke impervioussleeve overlying portions of said plug and said tobacco section forholding them in fixed relationship, said plug having a uniformcross-section substantially the same as that of the tobacco sectionthroughout its length and consisting essentially of a tow oflongitudinally extending thermoplastic fibers for passage of smoketherethrough from end to end and a porous paper plug wrap, closelyembracing and in non-spaced contacting relationship with the side wallsof said tow between the ends thereof, said plug having a plurality oflongitudinal, parallel, circumferentially spaced cavities, molded in thepaper plug wrap and the side wAll of said tow, said wrap being in 360*angle contacting non-spaced relationship with said sleeve for asubstantial portion of its length provIding a plurality of smokechannels defined by the interior surface of said sleeve and the exteriorsurface of said wrap extending from one end of said plug to a locationshort of the opposite end thereof whereby a portion of the smoke fromthe tobacco section passes through said tow from end to end of said plugand another portion of said smoke passes through said channels, saidporous plug wrap and a portion of the tow in said plug.
 13. Thecigarette recited in claim 12 wherein the porosity index of said paperplug wrap is between about 0.1 and 2 seconds.
 14. The cigarette recitedin claim 13 wherein the ratio of the exterior surface areas presented bysaid cavities in the plug to the exterior surface area of said one endwall is between about 1 to 1 and 15 to 1.